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Canaries got the unenviable job as coal mine air-quality monitors for good reason: birds are particularly vulnerable to changes in their environment. But environmental pollution may also affect songbirds in far more subtle ways. According to new research, heavy metal exposure from living close to a smelter changes the personality of great tits in ways that could impact their survival (Environ. Sci. Technol. 2019, DOI: 10.1021/acs.est.9b03548).

Andrea Grunst and her colleagues at the University of Antwerp correlated the behavior of great tits (Parus major), a common and relatively hardy European songbird, with heavy metal exposure. Over 2 years, the team looked at five populations living at different distances from a smelter in Antwerp, Belgium: 600, 2,500, 4,000, 5,000, and 8,500 m. For each bird, they measured arsenic, cadmium, copper, lead, and zinc concentrations in blood and feathers. The researchers then correlated individual birds’ levels with results from behavioral assays: one that measured how quickly the birds explored a novel environment and two others that measured different types of aggression.

Regardless of distance from the smelter, all the metals were detectable in the birds’ feathers, and lead, copper, and zinc were detectable in red blood cells. Overall, metal concentrations in the birds decreased as their distance from the smelter increased.

One behavior, novel environment exploration, decreased in the birds as blood and feather heavy metal concentrations increased, showing that “metal contamination from an industrial source has the potential to alter fundamental behavioral traits,” Grunst says. In the lab, researchers use this behavior as a proxy for personality variation among great tits. “Some tend to explore rapidly, indicating a bolder personality type, whereas others move around really slowly and seem to be shier,” she says. The behavioral differences likely reflect possible foraging strategies, suggesting this trait is inextricably linked to survival.

In humans, many studies have shown that heavy-metal exposure can cause neurological deficits. But proving anything beyond mortality in wild animal populations has proven more difficult. “We know in controlled, lab studies that these contaminants have effects on behavior, but observing them in wild populations is really challenging,” says Myra Finkelstein, a wildlife toxicologist at the University of California, Santa Cruz, who was not involved in the research.

The large sample size over multiple years gives the study heft, Finkelstein notes. But most interesting is the way that they were able to quantify something that has been difficult to pin down, she says. “Studies that look at sublethal impacts due to exposure are rare, so I was really excited to see this.”